In the continuous casting method of manufacturing steel, molten (liquid) steel from the steel-making operation or ladle metallurgy step is cast directly by a casting machine into semi-finished shapes (slabs, blooms, and billets). The terms “molten” and “liquid” are used interchangeably herein. The semi-finished shape is determined by the casting machine mold which receives the molten steel from a tundish and casts the steel into a steel strand with a molten inner core and an outer surface solidified by primary (water jacket) cooling within the mold. The strand is further subjected to secondary cooling upon exit from the mold until the entire strand is solidified at the time it is cut into slabs, blooms, or billets at the exit of the casting machine.
In the continuous casting process, the molten steel from the tundish flows into the mold through a submerged entry nozzle (SEN), which is connected to the outlet of the tundish, and the tundish is positioned so as to place the SEN into the mold to a selected depth. The flow of the molten steel from the tundish is gravity driven by the pressure difference between the liquid levels of the tundish and that at the top free surface of the mold. The flow is controlled by a stopper rod which partially blocks the tundish exit port, or a slide gate that moves across the inlet port of the SEN. As the steel enters the mold, the steel freezes against the water cooled walls and begins to form a shell, which is continuously withdrawn at the casting speed to produce the steel strand.
In such a process, the flow dynamics of the molten steel moving from the tundish to the mold can affect the quality of the continuous cast steel. The outlet ports of the SEN are below the liquid level in the mold. Turbulence and other transient phenomena in the molten steel exiting from the SEN into the mold may produce oxide inclusions and argon bubbles which other type inclusions may attach to, or high flow velocities may shear off droplets of mold slag into the steel flow where they become entrained in the liquid steel. Similarly, foreign particles trapped at the mold meniscus can similarly be entrained in the steel and generate surface defects and surface cracks. All of these produce inclusions that are product defects and result in product rejection and loss of manufacturing efficiency.
Such problems have a greater effect in thin slab casting, where inclusion entrapment due to the SEN-to-mold flow patterns occurs with a higher event frequency than in thick slab casting. This is due primarily to the thinner dimensions of the thin slab mold which require a higher flow velocity from a smaller geometry inlet nozzle to cast thin slab at the same throughput rate as thick slab. With thin slab casting, which is also known as Compact Strip Production, or CSP, the caster mold is too thin to permit a satisfactory submerged positioning of the nozzle inside the mold cavity. It is typically physically impossible for a CSP caster mold to accept a round SEN due to the narrow rectangular dimensions of the mold. Therefore, it is generally accepted by those skilled in the art of casting in a thin slab caster that the nozzle of the SEN has to be rectangular in shape to fit inside the mold.
An SEN may be manufactured having flow diverter parts such as flow dividers and baffles or flow diffusers in order to control the flow characteristics of the molten steel from the SEN into the mold. However, desired flow characteristics may be different for different types of molds.
Further limitations and disadvantages of conventional, traditional, and proposed approaches will become apparent to one of skill in the art, through comparison of such systems and methods with the present invention as set forth in the remainder of the present application with reference to the drawings.